An adjustable vibration damper which is marketed for, inter alia, motorcycles is known from US 2014/0116825 A1. In a motorcycle, the permissible overall length of the vibration damper is even more difficult to achieve compared with a passenger vehicle. It has turned out that an adjustable damping valve device having a conventional piston valve and, in addition, a parallel bypass opening as is shown in FIG. 13 of US 2014/0116825 A1is suitable for this specific application.
A coil which exerts an axial displacing force on an armature is arranged in an actuator housing on the piston rod side. A sliding sleeve which, with a valve sleeve fixed in the actuator housing, forms a slide valve is fastened to the armature. A return spring which preloads the sliding sleeve in a defined initial position is also arranged in the actuator housing.
Flow can occur in two directions in the slide valve. It is easy to recognize that dynamic pressure forces caused by an incident flow via the channel in the piston rod tenon exert an opening force on the slide valve. While there is indeed a static pressure compensation because the surface area impinged by pressure on the front side of the sliding sleeve is equal to that on the rear side of the sliding sleeve, the dynamic pressure force component in direction of the channel is appreciably greater than on the rear side of the sliding sleeve.
During an incident flow via the channels in the annular flange of the piston rod tenon, only mutually compensating radial forces act on the sliding sleeve. Consequently, there are substantial dynamic pressure force differences between the two incident flow directions. These differences in pressure force make it more difficult to configure, e.g., the return springs for the sliding sleeve in order to achieve a required damping force characteristic.
It is thus an object of the present invention to provide a damping valve device in which dynamic pressure forces influencing the opening behavior and closing behavior of the slide valve are minimized.